sorry for this most-likely super repeat thread. Did a search found nuthin', dont have much time to spend online here.

Set up a line using the 5 biner technique as seen on , http://www.youtube.com/watch?v=18qbgwCn2ZA

I've set it up just above knee hight. Its about 20 ft long. Cranking as hard as I can, it sags too the ground as soon as im a few feet away from the anchor.

So whats the obvious thing im missing here?

Many thanks.

There's no way you can get a line tight enough with the 5 crab system to walk at knee high levels. Certainly not with only one person tightening it. Set those at waist or higher for the kind of tension you can get with those. After a certain point, the amount of friction you have to overcome per inch of take is 4 or 5 times the force necessary to stretch the line an inch, in a friction free environment (that is, with a perfect 4-1 mechanical advantage).

You want knee high? Look into 3-1, 9-1, or 27-1 come-along systems (kind of like a hauling ratchet, but a bit more crude) if you want that level of tightness. I've been using a system that works at about knee height for years now, single person set up, but I don't use the 5 crab system. So there you go.

Yeah you can!! (although knee high is really low) It is totally easy and it only takes one person.

I use three biners on the tightening side and have good results, but you can use whatever pully-type tightening system you desire. The only requirement is that the webbing coming out of the tightening system must exit toward the tree it is attached to and that you have at least 10 feet of tail left on it.

Tie a slip knot in the webbing as close to the tightening system as you can. The loop on it only needs to be a couple of inches long. Now take the tail and put it around you and back through the loop in the slip knot. Hold onto the tail going out of the slip knot with one hand. Now walk to the other side of the tree (with the loop still around you) like this:

tree-slackline-tightening sys-tree-you

Place the loop of webbing around you somewhere underneath you butt. While holding the tail with one hand, put one foot and one hand against the tree and push. The line should tighten up very easily. Pull on the tail with your free hand to make the loop around your smaller to get another pull. When the slip knot reaches you, remove it and relocate it closer to the tightening system. Because you are mostly pushing with you legs and you legs are so much stronger than your arms, it is quite easy.

I have achieved a 75ft. waist high line using this method and I'm pretty sure you can get a line tighter this way than with 4-5 people just pulling on it.